Technical Abstract:
A sandwich method was developed for the detection of Salmonella in liquid eggs. Different out-break strains of Salmonella were used to inoculate liquid eggs at levels between 1 to 25 CFU/egg. Spiked eggs were then mixed with proper enrichment media before incubation at 37 C for 4 to 20 h. After enrichment, the bacteria were first captured by the use of immunomagnetic beads (IMB) coated with anti Salmonella antibodies. The captured bacteria were further labeled with samarium (Sm) conjugated anti Salmonella antibodies. Sandwiched Salmonella were then treated with fluorescence enhancement solution that contained a strong Sm chelator. The processes ranging from IMB capture to Sm chelation were performed using an automated KingFisher apparatus. The fluorescence intensity of chelated Sm was then measured by time-resolved fluorescence (TRF) for Sm. Using this approach, the presence of ~ 1 CFU of outbreak strains of Salmonella Enteritidis per egg (~50 g of liquid eggs) could be detected after enrichment for 20 h at 37 C. For higher levels of Salmonella Enteritidis contamination, e.g., 10 CFU per 50 g of liquid eggs, the enrichment time could be reduced to 5 h at 37 C. Thus, depending on desired sensitivity, the whole detection process could be completed either within an eight-hour shift or a twenty-four hour day. The results demonstrated that a combination of IMB capture and TRF measurement could be a rapid and sensitive method for Salmonella Enteritidis detection in liquid eggs.